1. Field of the Invention
The present invention relates to a resin-sealed power semiconductor device, formed by transfer molding, which is excellent in terms of productivity. The present invention particularly relates to a resin-sealed power semiconductor device, formed by transfer molding, which is small in size, realizes operation with a large current, and is highly reliable.
2. Description of the Background Art
A power semiconductor device capable of operating with a large current and a high voltage, which is able to efficiently discharge heat, which is generated by the operation of the power semiconductor device, to the outside of the power semiconductor device, is the one that is formed such that: power semiconductor elements are mounted on a substrate that includes a metal plate acting as a heat sink and a wiring pattern formed above the metal plate, the substrate including a ceramic plate interposed as an insulation layer between the wiring pattern and the metal plate; and heat-hardening resin is cast such that silicone gel is positioned between the heat-hardening resin and the substrate (see, e.g., Page 3, FIG. 1 of Japanese Laid-Open Patent Publication No. H08-316357 (hereinafter, referred to as Patent Document 1)).
However, in manufacturing of the power semiconductor device described in Patent Document 1, there are processes of, for example: bonding the external casing, which is formed of thermoplastic resin, to the metal plate; filling and curing the silicone gel; and injecting and curing the heat-hardening resin. Thus, there are a large number of manufacturing processes, causing a prolonged manufacturing time. Accordingly, there is a problem of low productivity.
A power semiconductor device which solves this problem and which is excellent in terms of productivity is the one in which: lead frames are provided on a metal plate while an insulation layer is interposed between the lead frames and the metal plate; and power semiconductor elements are mounted on the lead frames and sealed with transfer molding resin (see, e.g., Page 3, FIG. 1 of Japanese Laid-Open Patent Publication No. 2001-196495 (hereinafter, referred to as Patent Document 2)).
The power semiconductor device described in Patent Document 2, which is sealed with transfer molding resin, has a structure in which lead frames protrude, as external terminals, from the sides of the sealing resin of the transfer molding. Accordingly, there is a problem that it is difficult to reduce the size of the power semiconductor device. In addition, since a bending process is performed on the lead frames that are used as the external terminals, there is a limitation regarding the thickness thereof. For this reason, the amount of current to be applied to the external terminals cannot be increased. Thus, there is a problem that an increase in the current is limited in the power semiconductor device.
A power semiconductor device sealed with transfer molding resin, which is small in size and capable of increasing the current to be applied and solving the above problems, is the one in which: power semiconductor elements such as an IGBT and the like are mounted on a circuit pattern joined to a metal heat sink base; and main terminals and control terminals for external connection are joined to a circuit pattern surface so as to be substantially perpendicular to the circuit pattern surface, and are transfer molded.
A copper block, a cylinder having a screw hole, or a resin-molded nut, is used for a main terminal connected to a main circuit of the power semiconductor device. The main terminal that is a copper block is joined to external wiring by soldering. The main terminal that is a cylinder having a screw hole, and the main terminal in which a nut is resin molded, are connected to external wiring by bolts. Further, a female connector is used as a control terminal to be connected to a control circuit of the power semiconductor device, and is connected to external wiring by a pin-type terminal provided on a control substrate that is the external wiring.
In the power semiconductor device sealed with transfer molding resin, a bus bar to which a large current can be applied is used as the external wiring to be connected to the main terminal connected to the main circuit (see, e.g., Page 7 to 9, FIGS. 1, 5 and 10 of Japanese Laid-Open Patent Publication No. 2007-184315 (hereinafter, referred to as Patent Document 3)).
In the power semiconductor device described in Patent Document 3 which is sealed with transfer molding resin, the external wiring, which is a bus bar through which a large current can be applied to the main terminal, is fixed by thread connection or soldering. Accordingly, a substantial stress is applied to the main terminal area during the assembling of the power semiconductor device. Due to this stress, there is a problem that defects occur at the main terminal area, for example, a gap occurs at a joint surface between the outer side surface of the main terminal and the transfer molding resin, or fine cracks occur in the transfer molding resin. This causes problems of low yield, low productivity, and low reliability of the power semiconductor device. These problems are more prominent when the connection to the external wiring is formed by thread connection.
Further, since a large current is applied, even if a cable is used for external wiring to be connected to the main terminal, the cable used herein is highly rigid. Accordingly, the same problems occur.